1. Field of the Invention
The present invention is related generally to the field of internal combustion engine exhaust gas recirculation (EGR) for emissions improvement. More particularly, the invention provides an EGR system employing a fluidic pump receiving high energy primary air from a secondary pressure source for pumping of recirculated exhaust gas.
2. Description of the Related Art
EGR is a known method for reducing the NOX emissions in internal combustion engines. For effective use, an EGR system must overcome the adverse pressure gradient created by a positive pressure gradient across the engine. Various approaches to implementing EGR have included pumping of a portion of the exhaust gas from the exhaust manifold to the intake manifold. Pumping has been accomplished by introducing the exhaust gas into the compression inlet of a conventional turbocharger or supercharger present on the engine or, alternatively, providing a separate compressor receiving the exhaust gas and pressurizing it to a suitable pressure for insertion into the charge air downstream of the charge air boosting system on the engine.
Exhaust gases typically are corrosive or abrasive reducing desirability of introducing recirculated exhaust gas into the normal charge air boosting system due to damage or fouling of compressor or cooler components. Employing a separate compressor allows special configuration of the component to withstand the exhaust gas effects, however, such devices tend to be relatively expensive and reliability remains an issue.
Alternative designs for EGR incorporate fluidic pumping devices for obtaining pressurization of the recirculated exhaust gas flow. Use of the dynamic head of the exhaust gas stream for primary flow in such devices has typically been employed. The limited energy differential available for pressure amplification of the exhaust gas to be recirculated limits the effective capability of such devices. However, fluidic pumping avoids the cost and complexity of mechanical compression and components for such designs can be designed for robust tolerance to the exhaust gas effects.
It is therefore, desirable to provide a fluidic pumping system for EGR which incorporates a primary pumping gas flow with sufficient energy to provide the desired pressure amplification at flow rates sufficient to achieve recirculation of the exhaust gas at practical levels downstream of charge air boosting systems on the engine to avoid contamination of those systems.